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I'd say pretty much anything you want to use. You can run your disk across a wax candle to keep it from loading up to much.

Personally I wouldn't worry about contaminants on a skeg. Your most likely going to see black crap floating out of the base aluminum.

If the lower unit still has the prop shaft and gear housing seals in it that would be more of a concern. Use high heat to get the weld going quick and let it cool some when it gets hot. Maybe some wet towels will help cool the gear housing.

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Yeah I was wondering what to use..my aluminum oxide flappers embed the aluminum(I wax them too),I found 3M surface conditioning disks work.Just looking for some tricks here.How about cutting the skeg material and the lower unit..I use my plama on thr cast,but saw cut the blanks...any thoughts?

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There are grinder discs made specifically for aluminum you could try instead of the flap discs. These do not load up like the standard type disc do. Check at your LWS for them, someplaces you may have to ask them about it as they don't always keep them out on the shelf.

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Hello, I have had good luck using flapper or sanding disks to remove the paint off the lower units. Once the paint is gone , regular grinding wheels or zip-cuts with bees wax to stop them clogging up for grinding or cutting the base aluminum. As for cutting the new patch pieces or material , I use a small wood cutting bandsaw for making up patch pieces or shape cutting, its alot cleaner cut than the plasma and there is no cleanup required, before welding it. You can even bevel your pieces nice if you want to get real fancy. For just breaking up the oxide layer and between passes i use a blue Walter stainless steel wirewheel on the grinder for buffing off the welds. This works good if you do get the black junk contamination . hope this helps

I have a welding addiction

...the only stupid question is the one you didn't ask

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Thanks for the tips...I found my plasma left a roughish edge there too,the band saw idea is great-that should help things go ceaner & maybe bevel at the same time.My buddy sandblasts the paint off-I'm not so sure about doing that tho, with the silica sand.Things usually go pretty well,but we are still dealing with cast aluminum of varying qualities.

So what do guys like for skeg material?I use either 5053,6061,but am wondering about the pre-cast ones.Sure seem expensive but maybe savings can be had from less shaping time.Are these pre-cast skegs free of junk inside them?

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The replacements are probably cleaner metal than the original. Kind of like aluminum props, some are clean and some are trash. Don't worry too much about a skeg. Get some aluminum filler paste for any pinholes that may not sand out.

If its not to bad, straighten it with a hammer ( a heavy soft hammer) over something to provide backing support and just weld it out, then finish it down to the original look.

If its over half gone, that may not be an option. You need these things removed from the engine where you can work on it. If its broken off up close to the housing, seals will most likely need to be replaced afterwards, tell the owner so they know ahead of time.

I have welded them for a prop shop, it is not that bad. Don't overthink it and worry with it. Don't know what your welding it with but you'll need some power if its up in the thicker area.

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Yeah I've played around on corroded cast aluminum,sure shows up some interesting things!lol!I was using a Precision Tig 225,but not enough power,welds good,harsh arc however.So I just ordered a Synchrowave 250dx,I tried an older one at work & liked it.Just as mentioned,the need to puddle fast on thick sections to lower overall heat input will be great.So far none (skegs) have fallen off leaving the dock..lol!Some that have been re-hit bent over & didn't break,happy about that.The biggest gearcase so far was a 150hp,but I didn't have to replace much.Ok I appreciate the advice & need one more opinion(for now).Where do you ground the welder on gearcase?Is there anything to the idea that current thru the bearings is bad?I was given two differing opinions around here

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Yeah I've played around on corroded cast aluminum,sure shows up some interesting things!lol!I was using a Precision Tig 225,but not enough power,welds good,harsh arc however.So I just ordered a Synchrowave 250dx,I tried an older one at work & liked it.Just as mentioned,the need to puddle fast on thick sections to lower overall heat input will be great.So far none (skegs) have fallen off leaving the dock..lol!Some that have been re-hit bent over & didn't break,happy about that.The biggest gearcase so far was a 150hp,but I didn't have to replace much.Ok I appreciate the advice & need one more opinion(for now).Where do you ground the welder on gearcase?Is there anything to the idea that current thru the bearings is bad?I was given two differing opinions around here

Its usually best to ground as close to where your actually gonna weld, I try to usually put the clamp on the actual fin , that way there is much less chance of any arcing out of bearings etc. I know there are some that would not even think of welding without stripping the whole lower end, but if you are careful and develop a procedure for controlling the heat, its easy work. once you get your piece tacked on good you can maneuver the ground to get it out of the way of welding. I have had a couple where i had to tack a grounding tab of scrap aluminum very close to the edge of the actual weld joint zone, that way there are no random spots or arc strikes on the gear case.

I have a welding addiction

...the only stupid question is the one you didn't ask

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Thats a great idea about a ground tab.Grounding to the fin makes a lot of sense too,I am doing this now,but I've seen some guys ground to the prop shaft,handy but....My thoughts were getting juice from arc to ground away from bearings not thru them.Just one less thing to think about.A friend is a licensed marine mechanic and he says welding on empty gear cases is tricky -easy to oval the bearing bores.So I have been leaving grease in & taking my time to let cool down.It sounds like you have done a lot of aluminum work,I am enjoying learning how to weld the stuff.Do you ever weld skegs on with gearcase still attached to engine?

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I usually get guys bringing them to me right after they found rocks or reefs... I have done a lot with everything attached, the big thing is to not pound too much heat into the casing while you are welding, and also to control your interpass temperatures. I have a bunch of beach type towels i soak in water , and then place on the actual bearing bore area of the lower leg. you have to be careful with wet stuff and AC high frequency welding if you get my drift. Between passes i usually put another towel right on the weld area. This heat conducts out very fast so it doesn't take long to cool everything down quick. i occasionally use the IR thermometer to keep track off how hot, but i have done enough that touching them bare handed tells me how much welding a guy can get away with between "coolings" make sure you dry the metal off good before you start welding again also. the moisture hitting the molten aluminum puddle is neat to watch , but crappy to repair. Best usually to keep as cool as you can, no boiled out gear oil and rubber seals get cooked that way.

I have a welding addiction

...the only stupid question is the one you didn't ask

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I just thought about your comment of what some guys do. I would never ground to the actual prop shaft. Aside from the bearings and the possibility of the bearing failing due to arcing out, the splined ends of the shaft can end up doing the same thing when fitted to their mating parts. a nice small gap of a couple thousandths of an inch between the high and lows of the splined parts could also cause similiar conditions. If one of the splines gets flash hardened it can become brittle and shatter . Usually this would cause the whole thing to pile up like a broken tooth on a gear, i saw a shaft that failed and this appeared to be the cause. you could actually see the temper colors on the shaft where the failure occured.

I have a welding addiction

...the only stupid question is the one you didn't ask

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Great info -I can't wait to try this stuff...I always wondered why the gearcases were removed around here.Maybe I can save the boat owner some money doing it attached to motor.The damp towel idea is perfect.I'm glad I'm not the only one to be wary of HF shocks!I just finished an outboard test tank & got HF blasted(my fault) half inside the thing.Gotta be careful thats for sure.What kind of interpass temp we talking about?I need more experience to "just know",I have a IR temp gun too.Hopefully the 250dx will allow me to puddle faster & reduce heat soak.What welder are you using?